Doors for closing an opening in an aircraft fuselage usually comprise a stiffened outer shell designed in such a manner that in its closed state the door forms a harmonious surface with the exterior of the fuselage. The stiffening structure covers an extensive area of an interior of the outer shell; its design is dictated by the fuselage structure and comprises longitudinal and transverse stiffening elements that are connected to the outer shell.
An edge region, which extends in close proximity to the exterior edge of an inner side of the outer shell, comprises a door seal that when the door is closed seals the aircraft cabin from the surroundings. Usually, the door seal rests directly against the outer shell and comprises a seal profile that, supported by holding profiles, is bulged. With the door in its closed state the seal profile adapts to a corresponding sealing face in or on the door opening.
In the design of aircraft components many parameters are taken into account, including, among others, the weight, stiffness, fatigue strength, ease of manufacture, and certification guidelines. Any alteration in the stiffening structure, for at least partial increase in the stiffness of the aircraft door, would necessitate renewed certification with its associated relatively high costs.